1. Field of the Invention
This invention relates to the field of a test apparatus for head gimbal assemblies for hard disk drives. More particularly, this invention relates to the field a head gimbal assembly test shaker for resonance testing of head gimbal assemblies, having improved system mode performance.
2. Description of Related Art
Magnetic hard disk drives used for data storage typically included a head gimbal assembly (HGA) which carries a slider which includes a read/write transducer for writing data to, and reading data from, the disk surface. As recording track densities increase and servo bandwidths also increase, there is a need to test HGA resonance and other dynamic characteristics at high frequencies. U.S. Pat. No. 7,034,372, assigned to the assignee of the present application and hereby incorporated in its entirety, discloses a HGA dynamics tester which uses a piezoelectric device to drive the HGA for resonance testing. FIGS. 1 and 2 herein illustrate such a prior art dynamic tester. Test assembly 10 comprises a mounting plate 12, a piezoelectric (PZT) crystal actuator 14, and a load plate 16. Mounting plate 12 and load plate 16 are typically made of 440 C stainless steel. Epoxy (not shown) is used to adhere the parts together.
The shaker is mounted to the test assembly holder via an electromagnet. This requires a ferrous material on the bottom surface of the mounting plate 12. The 440 C material is sufficiently ferromagnetic for this purpose. Different mounting methods are possible, and may require a high wear surface such as a tooling steel for low cost and high life.
During test, PZT 14 is driven horizontally, i.e., in shear, in either the x or y direction. Typically, the resonance behavior of HGA 18, which is the unit under test (UUT), is tested by sensing the position and velocity of various parts of the HGA using a laser Dopper vibrometer (LDV) and correlating the output movement to the input movement, in order to calculate the frequency response of the UUT. As areal density increases the disk drive data track sizes shrink, the resonance performance of the HGA becomes more critical, and accurately measuring the resonance performance of the HGA likewise becomes more critical.